The accusative can sometimes be used to demonstrate intensive force... i.e. "bonam fortunam!" (good luck!). I am not sure if this is the case here or if it is an implied verb, which I have also seen in many quotes. Perhaps someone else will grace you with a more detailed answer before your time is up ^.^

Thanks for the help. I understand the construction now. The problem was, I did not know about the accusative in exclamations before. I've had a look in my grammar, and I understand it now. Thanks again.